The present invention relates to the widening of hollows made of metal, particularly steel tubes, under utilization of a multielement outer tooling and sealing the front faces of the hollow so that on the inside a strong hydraulic pressure can be produced to obtain the widening whereever and to whatever extend needed. Moreover, the invention relates to equipment for providing this widening under utilization of particularly configured sealing heads interconnected through tie-rods.
Hollow or hollow sections of the kind to which the invention pertains and which are processed in accordance with the invention are basically tubular elements made of metal particularly steel which may have any kind of cross section, in other words emphasis is on elongated configuration basically cylindrical or curved ones but with any kind of cross section.
Frequently in technology, civil engineering or the like, parts are needed which are basically of an elongated configuration, either straight but also curved ones are of interest and having a cross section that may vary drastically along the length extension. For reasons of weight such construction parts are often made as hollows or tubes simply because the strength requirements do not require solid configuration. Here then it was suggested, particularly for limiting expenditure in the making process to provide basically a tubular blank and to change the configuration of the blank through local control widening.
German patent No. 29 35 086 discloses a method and equipment wherein a tube is subjected to an internal hydraulic pressure forcing the tube's wall locally against an outer rigid tube. The deformation is supported in addition by axial pressure acting on the tube being deformed and in addition to the hydraulic internal pressure. In the beginning of the deformation, the hollow is completely enveloped in the so called guiding tube except for the central part. These guiding tubes are gradually retracted in axial direction during the deforming so that progressively increased actual region of deformation is made of available for that purpose, not at once but in a graduated fashion.
The open front faces of the hollow being deformed are sealed through piston-like elements having appropriate sealings. The pistons are inserted in the hollow and provide, in addition, supplemental axial pressure. Further sealing is established through the guiding tubes which in turn envelops the piston rods. The sealing effect is not changed in principle as the guiding tubing is gradually retracted for the aforestated purpose. This known method and equipment as outlined above rather rudimentarily is actually very expensive and complex. Moreover it is not suited for processing blanks towards obtaining a curved or even angled off component. On the other hand it has to be considered that the disposition of sealing for obtaining the hydraulic expansion requires a very accurate treatment of the sealing surfaces and a very accurate tuning of the piston geometry in relation to the hollow blank. Tolerances whatever and whereever they are, may readily lead to problems of an unforeseeable nature in the working stage as far as resulting in unforeseeable deformations are concerned.